U.S. patent number 6,472,062 [Application Number 09/446,308] was granted by the patent office on 2002-10-29 for method for making a non-sticking diamond-like nanocomposite.
This patent grant is currently assigned to N.V. Bekaert S.A.. Invention is credited to Dominique Neerinck, Peter Persoone, Marc Sercu.
United States Patent |
6,472,062 |
Neerinck , et al. |
October 29, 2002 |
Method for making a non-sticking diamond-like nanocomposite
Abstract
An improved non-sticking diamond-like nanocomposition includes
networks of a-C:H and a-Si:O, wherein the H-concentration is
between 85% and 125% of the C-concentration. The composition
includes preferably 25 to 35 at % of C, 30 to 40 at % of H, 25 to
30 at % of Si, and 10 to 15 at % of O.
Inventors: |
Neerinck; Dominique
(Hertsberge, BE), Persoone; Peter (Deinze,
BE), Sercu; Marc (Roeselare, BE) |
Assignee: |
N.V. Bekaert S.A. (Zwevegem,
BE)
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Family
ID: |
8228458 |
Appl.
No.: |
09/446,308 |
Filed: |
December 20, 1999 |
PCT
Filed: |
June 15, 1999 |
PCT No.: |
PCT/EP98/03726 |
371(c)(1),(2),(4) Date: |
December 20, 1999 |
PCT
Pub. No.: |
WO98/59089 |
PCT
Pub. Date: |
December 30, 1998 |
Foreign Application Priority Data
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Jun 19, 1997 [EP] |
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97201867 |
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Current U.S.
Class: |
428/336;
427/249.11; 427/249.7; 427/534; 427/535; 427/577; 428/446 |
Current CPC
Class: |
C23C
16/0236 (20130101); C23C 16/26 (20130101); C23C
16/401 (20130101); C23C 16/505 (20130101); A61B
18/085 (20130101); A61B 18/1442 (20130101); A61B
2017/0084 (20130101); Y10T 428/265 (20150115) |
Current International
Class: |
B32B
5/16 (20060101); B32B 9/04 (20060101); C01B
31/02 (20060101); C01B 31/00 (20060101); C23C
16/26 (20060101); C23C 14/02 (20060101); C23C
16/02 (20060101); C23C 16/30 (20060101); C23C
16/42 (20060101); H05H 1/00 (20060101); B32B
005/16 (); B32B 009/04 (); C23C 016/26 (); C23C
014/02 (); H05H 001/00 () |
Field of
Search: |
;428/220,411.1,332,334,446,447,923,926,932,336 ;520/10,12,30-37
;427/534,535,577,249.7,249.11 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 856 592 |
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Aug 1998 |
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EP |
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95/24275 |
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Sep 1995 |
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WO |
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97/12757 |
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Apr 1997 |
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WO |
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97/40207 |
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Oct 1997 |
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WO |
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Other References
Dorfman, Benjamin et al., New Diamond and Diamond-Like Films, vol.
6, "Diamond-Like Nanocomposite Coatings: Novel Thin Films", pp.
219-226, (1995). .
Dorfman, V.F., Thin Solid Films, 212, "Diamond-like nanocomposites
(DLN)", pp. 267-273, (May 15, 1992)..
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Primary Examiner: Thibodeau; Paul
Assistant Examiner: Ahmed; Sheeba
Attorney, Agent or Firm: Foley & Lardner
Claims
What is claimed is:
1. An improved non-sticking diamond-like nanocomposition comprising
networks of a-C:H and a-Si:O, wherein the H-concentration is
between 85% and 125% of the C-concentration, and wherein the
nanocomposition has a hardness of at least 10 GPa as measured by
nanoindentation.
2. A composition according to claim 1 comprising 25 to 35 at % of
C, 30 to 40 at % of H, 25 to 30 at % of Si and 10 to 15 at % of
O.
3. A composition according to claim 1 which is doped with at least
one transition metal.
4. A composition according to claim 3 wherein said transition metal
is Zr, Ti or W.
5. A composition according to claim 1 comprising 0.5 to 5 at % of
an inert gas.
6. A substrate, covered at least in part with a layer of the
composition according to claim 1, wherein the thickness of the
layer is between 0.01 .mu. and 10 .mu.m.
7. A substrate according to claim 6, wherein said substrate is a
moulding mean.
8. A substrate according to claim 6, wherein said substrate is a
mould for injection moulding of polymer materials.
9. A substrate according to claim 6, wherein said substrate is an
electrode for welding plastic by fusion.
10. A substrate according to claim 6, wherein said substrate is an
electro-surgical cutting blade.
11. A process for coating in a vacuum chamber a substrate at least
in part with a diamond-like nanocomposite composition, comprising
the steps of: a) plasma etching of the substrate by bombardment of
the substrate by ions of an inert gas; b) introducing in the vacuum
chamber, at a working pressure of between 5.times.10.sup.-3 and
5.times.10.sup.-2 mbar, a liquid organic precursor containing the
elements C, H, Si, O to be deposited in proportions, which
proportions remain substantially constant during a deposition
process; c) forming a plasma from the introduced precursor by an
electron assisted DC-discharge using a filament with a filament
current of 50-150 A, a negative filament bias DC voltage of 50-300
V and with a plasma current between 0.1 and 20 A; and d) depositing
the composition on the substrate, to which a negative DC-bias or
negative RF self-bias voltage is applied, in order to attract ions
formed in the plasma, wherein the frequency of the RF voltage is
between 30 and 1000 kHz, wherein the diamond-like nanocomposite
composition comprises networks of a-C:H and a-Si:O, wherein the
H-concentration is between 85% and 125% of the C-concentration, and
wherein the diamond-like nanocomposite composition has a hardness
of at least 10 GPa as measured by nanoindentation.
12. A process according to claim 11, wherein the organic precursor
is an organosilicon compound.
13. A process according to claim 12, wherein the organic precursor
is hexamethyldisiloxane.
14. A process according to claim 11, wherein during the deposition
process an inert gas is introduced in the vacuum chamber, ionised,
and incorporated by ion bombardment into a growing composition
layer on the substrate.
15. A process according to claim 11, wherein the precursor is mixed
with a carrier gas for introduction in the vacuum chamber and the
mixture is heated to evaporate the precursor.
16. A process according to claim 15, wherein the carrier gas
comprises an inert gas.
17. A process according to claim 11, wherein at least one
transition metal is co-deposited on the substrate by one of ion
sputtering and thermal evaporation.
18. A process according to claim 11, wherein the substrate is a
mould used for injection moulding of polymer materials, which is
coated at least in part with the non-sticking diamond-like
nanocomposite composition.
19. A process according to claim 11, wherein the substrate is an
electrode for welding nylon by fusion, which is coated at least in
part with the non-sticking diamond-like nanocomposite
composition.
20. A process according to claim 11, wherein the substrate is an
electrosurgical cutting blade, which is coated at least in part
with the non-sticking diamond-like nanocomposite composition.
21. A process according to claim 11, wherein, in the step of
depositing the composition, the negative DC-bias or negative RF
self-bias voltage is between approximately 350 and 700 V.
Description
FIELD AND BACKGROUND OF THE INVENTION
The invention relates to an improved non-sticking diamond like
nanocomposite composition. The substrate surfaces thereby obtain
non-sticking properties, and become at the same time very hard,
corrosion and wear resistant and self-lubricating. The invention
also relates to certain uses of such coated substrates e.g. as
moulding means.
Diamond Like Nanocomposite (DLN) compositions consist of an
amorphous random carbon network which is chemically stabilized by
hydrogen atoms. The carbon network is interpenetrated with an
amorphous glass-like silicon network which is chemically stabilized
by oxygen atoms (a-C:H/a-Si:O).
In U.S. Pat. No. 5352493 a process is described for coating a
substrate with a DLN composition in a vacuum chamber. Thereby a
plasma is formed from an organic precursor containing the elements
C, H, Si and O to be deposited in a certain proportion. This
composition is deposited from the plasma onto the substrate to
which a negative DC-bias or RF self-bias voltage is applied.
Most of the conventionally applied deposition processes use high
RF-voltage frequencies (up to 25 MHz, typically 13,56 MHz). This
renders the upscaling of the process quite difficult.
Moreover, in some known processes very low pressures (less than
3.1.sup.-4 mbar) are applied, making it difficult to apply a
homogeneous coating, in particular on a substrate with a complex
shape. It is however of great interest with regard to the
industrial application of the homogeneous coatings--also on complex
parts--to eliminate the need for very complex rotating substrate
holders.
An improved DLN coating, deposition process and reactor design are
described in applicant's copending patent applications Nos.
WO/97/40207 and EP 856 592.
OBJECTS AND DESCRIPTION OF THE INVENTION
It is an aim of the invention to provide a non-sticking homogeneous
DLN composition and a flexible process for uniformly coating any
substrate with such composition. With a non-sticking coating
composition is meant here a DLN offering a surface energy of
between 22 and 30 mN/m. It is also an object to provide such a
coating with a hardness above 10 GPa.
According to the findings of the inventors, such a non sticking DLN
coating needs a relatively high concentration of hydrogen. In
particular the H-concentration should be between 85% and 125% of
the C-concentration. The composition preferably comprises from 25
to 35 at % C, 30 to 40 at % of H, 25 to 30 at % of Si and 10 to 15
at % of O.
The coating method comprises the steps of a) plasma etching of the
substrate by bombardment of the substrate by ions of an inert gas
such as Ar (Reactive Ion Etching, RIE), b) introducing in the
vacuum chamber, which operates at a working pressure of between
5.10.sup.-3 and 5.10.sup.-2 mbar, a liquid organic precursor
containing the elements C, H, Si, O to be deposited in suitable
proportions, which proportions remain substantially constant during
the deposition process, c) forming a plasma from the introduced
precursor by an electron assisted DC-discharge using a filament
with a filament current of 50-150 A, a negative filament bias DC
voltage of 50-300 V and with a plasma current between 0.1 and 20 A,
d) depositing the composition on the substrate, to which a negative
DC-bias or negative RF self-bias voltage of 350 to 700 V is
applied, in order to attract ions formed in the plasma; the
frequency of the RF voltage being preferably comprised between 30
and 1000 kHz.
The plasma etching step a) of the proposed coating method activates
the surface and removes residual oxydes from it. This process step
is essential for obtaining a good adherence of the coating onto the
substrate.
The liquid organic precursor is preferably a siloxane compound such
as hexamethyldisiloxane (HMDS), with a relatively high content of
Si and O. A polyphenylmethylsiloxane, with a lower content of Si
and O, can however also be used as precursor.
Although the use of a filament, e.g. a thoriated W filament, is not
necessary for forming the plasma, an electron assisted DC discharge
leads to a higher plasma density and thus to a deposition rate
which is at least 20% higher than that without use of the filament.
The bias voltage influences the properties of the deposited
coatings, especially the hardness and the surface energy. The lower
the bias voltage, the lower the hardness of the coating (e.g. 12
GPa at 500 V bias voltage, compared to 8 GPa at 300 V bias
voltage), and the lower the surface energy. The non-sticking
properties of the deposited coatings are indeed better when the
coating is deposited at lower bias voltages.
The low RF frequency used in step d) of the proposed coating method
facilitates its upscaling.
In a vacuum reactor as described in applicant's copending
application WO 97/40207 the precursor is introduced with Ar as a
carrier gas. The mixture gas/precursor is delivered in a
controllable manner to the vacuum chamber through a controlled
evaporation mixing system. The liquid precursor is passed through a
liquid mass flow controller to a mixing valve where it is combined
with the carrier gas stream. From there it is transferred to a
mixing chamber which is heated to about 80.degree. C. to
200.degree. C. The precursor evaporates in the mixture and the hot
mixture enters the vacuum chamber.
The working pressure in the vacuum chamber is typically about
5.10.sup.-3 to 5.10.sup.-2 mbar, which is much higher than the
pressures being applied in some known processes, favouring a more
homogeneous deposition on complex substrates. This working pressure
range is preferably between 7.10.sup.-3 and 1.2.10.sup.-2 mbar.
The non-sticking properties of the coating can be expressed in
terms of its (low) surface energy and the (high) contact angle of a
water droplet on it.
The contact angle of a water droplet on a surface coated with the
DLN composition according to the proposed method, has been measured
to be 90 to 95.degree. . The surface energy of the deposited DLN
coatings typically varies between 25 and 30 mN/m. The surface
energy has been determined from the contact angles of certain
liquids (demineralized water, formaldehyde, ethylene glycol,
hexane) on the coated surface, using a Zisman plot.
If a magnetic field between 5 and 150 Gauss is applied during the
deposition of the coating, the plasma is intensified. The magnetic
field can be applied e.g. by means of an inductive coil, situated
near the thoriated filament in the reactor.
During the deposition process according to the invention, an inert
gas can be introduced in the vacuum chamber, ionised and
incorporated by ion bombardment of the growing layer. This may lead
to a higher nanohardness of the deposited film. The inert gas can
be introduced separately or as carrier gas for the precursor.
If desired, one or more transition metals can be codeposited by ion
sputtering or by thermal evaporation in order to influence the heat
and/or electrical conductivity of the coating.
An example of a coating composition deposited according to the
proposed method is as follows: 36% Si, 17% O, and 47% C (leaving H
out of consideration). Its surface energy measured 27 mN/m.
In order to lower the surface energy of the deposited coating even
more, additional oxygen gas can be added to the. plasma during the
coating process. By adding an additional flow of oxygen so that an
O-content of 25 to 30% is reached (leaving H out of consideration)
an even lower surface energy of 24 mN/m was measured.
The non-sticking, homogeneous DLN coating displays a low surface
energy, a high nanohardness, good tribological properties (even
under humid conditions), and a controlled heat and/or electrical
conductivity.
The composition can be doped with at least one transition metal,
such as Zr, Ti or W. The plasma etching step can result in the
incorporation into the composition of 0.5 to 5% at of an inert gas,
such as Ar, Kr or N.
The coating can therefore be considered as a hard equivalent of
teflon, having however a wear resistance far in excess of that of
teflon. It is indeed a very important disadvantage of teflon that
it is not hard enough to withstand strong mechanical forces.
The proposed non-sticking DLN coating has the additional advantage
with respect to teflon that it does not contain any fluorine.
The non-sticking properties of the deposited DLN coating, make it
very suitable for many applications, i.a. for those as described in
the following examples. The thickness of the coating layer on the
substrate is chosen between 0.01 .mu.m and 10 .mu.m. The invention
provides in particular all kinds of moulding means with e.g. male
and female parts ; in the form of shaping pens, pins, pointers,
nozzles, dies, stamps and stamp pads etc. The moulding surface of
these means is then the substrate onto which the non-sticking DLN
coating of the invention is deposited.
EXAMPLES
Example 1
Hard Release Coating for Moulds Used in the Injection Moulding
Process
By means of the coating method according to the invention, a
non-sticking DLN coating has been successfully applied onto the
surface of a mould used for the injection moulding of
polyoxymethylene (POM). The adherence of the coating to the
substrate was very satisfying, as were the demoulding results in
general: no material sticked to the mould when releasing it. The
release from the DLN coated mould was much faster than from the
non-coated moulds, and no material deformation was observed when
removing the moulded articles from the mould. The coating is also
useful for mould surfaces for shaping other polymer or other pasty
materials by methods such as injection moulding, extrusion,
pultrusion or press moulding.
Example 2
Release Coating for an Electrode for Welding Nylon by Fusion
In the nylon welding process, two nylon muff-like workpieces are
contacted at their ends with each other. A wire is inserted along
and within the central cavity of these two pieces. The wire is then
heated by induction or by means of electrical resistances (Joule
effect), causing the nylon material in the contact area to melt.
Afterwards, when starting to cool down, the wire is pulled out of
the nylon workpieces. The nylon material solidifies upon cooling,
so that the two workpieces are welded together.
The hot nylon material may in no way stick to the heating wire when
pulling it out. This can be prevented by coating the wire with a
non-sticking DLN film by means of the method according to the
invention.
Commonly a teflon coating is used for this purpose. However, teflon
cannot withstand the great mechanical (wear) forces acting on the
coating when pulling it out of the cavity. As the tribological
properties of the DLN coating are better than those of teflon, and
as the DLN coating is much harder than the teflon equivalent, it is
more suitable than teflon for this application. Indeed the DLN
coated electrode is more durable and thus re-usable for a great
number of times.
Example 3
Non-Sticking Coating on Electro-Surgical Blades
In one method for surgical cutting of the human skin or tissue use
is made of an electro-surgical cutting blade. Thereby a RF voltage
is applied to heat up said blade. The human body acts as the earth
pole, so that an electrical current passes through the body, and
burns skin or tissue open.
The coating method according to the invention can be used for
depositing a non-sticking DLN coating onto the surface of the
cutting blade, preventing human tissue or blood from sticking to
it.
Various cutting tests were performed on liver and mozzarella cheese
simulating the human tissue.
For the mozzarella cutting test a Valleytab Force2 ES generator and
power control pencil were employed. The cheese was placed on the
return electrode (metal plate) and the coated cutting blade was
plugged into the pencil tip. A RF power of 25 W/500 kHz was
applied.
The cutting results with respect to the DLN coated blades are
excellent. The coated blades perform at least as well as the
commonly used teflon-coated ones.
Furthermore, the non-sticking DLN compositions show promising use
as coatings on means for processing food, plastics and
pharmaceuticals, detergents and other liquid or pasty
materials.
* * * * *